This invention relates generally to centrifugal compressors and is more particularly concerned with the installation of a silencer arrangement within the collector of the centrifugal compressor.
Centrifugal compressors are frequently incorporated in large air conditioning systems. These compressors have a number of components that generate sound and vibration, such as the motor, gearing, impeller, diffuser, condenser, cooler and discharge lines. Besides design considerations to reduce sound generation at their sources, it is conventional to reduce sound with sound absorbing silencers, such as external, surface applied materials. It is also the practice to install internal silencers in the discharge line of the compressor. These silencers employ an acoustically absorbent material such as glass fibers, mineral fibers, Dacron or other natural or synthetic material. These devices are usually installed within the discharge pipe of the centrifugal compressor by welding or otherwise securing a silencer assembly to the inner sidewalls of the discharge pipe. Because of the relatively small size of the discharge pipe and the shortage of possible axial locations to install the silencer, the applicability of their approach has been severely limited. Further, when welding is carried out in positions adjacent to the absorptive material within the silencers, the sound absorbing material can be damaged from the resulting heat. Further, the silencer in the discharge pipe causes additional pressure drop due to blockage, resulting in higher power for a given cooler and condenser pressures.
An alternative to this approach is simply to replace a portion of the discharge pipe with a replacement section that incorporates a silencer device. These replacement sections require special attachment structure, such as mating flanges, and thus become relatively expensive because of excessive requirements for time and materials to construct them.
A more recent approach is to install a sound absorbing silencer within the compressor, so that most of the noise can be absorbed as close to the dominant noise source as possible. To do this, a preferred approach has been to locate sound absorbing material into the annular discharge chamber, or volute, of the compressor. However, it is difficult to install the absorptive material inside the volute, and even more difficult to secure the material in circumferentially spaced locations within the volute. Because the volute is a pressure containing chamber, installing the silencers through holes penetrating the chamber walls could result in unacceptable losses of the compressed refrigerant. Also because the housing of the compressor, including the discharge chamber, is typically formed of cast iron, welding the silencer devices to the walls of the discharge chamber is impractical. Adhesives can be impractical a well because of incompatibility with the refrigerants, and lack of strength and reliability. Additionally, the silencer arrangement should be positively retained to prevent any movement by the refrigerant flowing past the silencer.
A previous proposed solution to this problem is described in U.S. patent application Ser. No. 07/656,537 filed Feb. 19, 1991, having a common assignee herewith. In that approach, silencer elements, i.e. flat silencer, pans, are installed against a radially extending wall of the discharge chamber or volute, prior to the final assembly of the compressor diffuser apparatus. In that technique, a ring is installed into an annular channel on the inner circumference of the discharge chamber. Leaf spring clips are attached to this ring and bias against the sound absorbing silencer pans. Flexibility in these springs allows for a minor amount of positional adjustment as the silencer pans bed themselves in against the discharge chamber wall. However, this construction can actually generate some noise. The silencer pans can vibrate against the chamber wall and springs because of flow-induced vibrations as the compressed gas passes over the springs. Because of relative motion between the ring and silencer pans, wear occurs in the anti-rotation pins that keep the ring in place in the annular channel. Wear can also occur in the springs and pans. This wear can lead to further loosening of the silencer pans.
It is desired to secure the silencer pans within the discharge chamber or volute in a manner that facilitates installation and avoids the foregoing problems caused by flow-induced vibrations. That is, it is desired to improve the fastening of the silencer pans and increase the reliability of the silencing arrangement.
Accordingly, it is an object of this invention to provide an improved silencer assembly for a centrifugal compressor, which avoids the drawbacks of the prior art.
Another object is to provide for securing of the silencer in a fashion that avoids flow-induced vibration.
A further object is to provide for direct attachment onto the wall of the compressor discharge chamber which avoids leakage of compressed refrigerant.
Still another object is to provide fastening means for the silencer pans which are as simple and straight forward as possible.